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Bug fix: small values of max_bin cause program to crash #2299

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merged 6 commits into from
Aug 16, 2019
Merged

Bug fix: small values of max_bin cause program to crash #2299

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fe5c8e2
Fix bug where small values of max_bin cause crash.
btrotta Jul 31, 2019
439bcfd
Revert "Fix bug where small values of max_bin cause crash."
btrotta Jul 31, 2019
4c28a32
Fix bug where small values of max_bin cause crash.
btrotta Jul 31, 2019
1ede99d
Reset random seed in test, remove extra blank line.
btrotta Aug 1, 2019
e471f9a
Minor bug fix. Remove extra blank line.
btrotta Aug 1, 2019
fddc8c2
Change old test to account for new binning behavior.
btrotta Aug 1, 2019
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23 changes: 17 additions & 6 deletions src/io/bin.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -177,11 +177,10 @@ namespace LightGBM {
left_cnt = num_distinct_values;
}

if (left_cnt > 0) {
if ((left_cnt > 0) && (max_bin > 1)) {
int left_max_bin = static_cast<int>(static_cast<double>(left_cnt_data) / (total_sample_cnt - cnt_zero) * (max_bin - 1));
left_max_bin = std::max(1, left_max_bin);
bin_upper_bound = GreedyFindBin(distinct_values, counts, left_cnt, left_max_bin, left_cnt_data, min_data_in_bin);
bin_upper_bound.back() = -kZeroThreshold;
}

int right_start = -1;
Expand All @@ -192,16 +191,27 @@ namespace LightGBM {
}
}

if (right_start >= 0) {
int right_max_bin = max_bin - 1 - static_cast<int>(bin_upper_bound.size());
CHECK(right_max_bin > 0);
if (bin_upper_bound.size() == 0) {
if (max_bin > 1) {
bin_upper_bound.push_back(kZeroThreshold);
}
} else {
bin_upper_bound.back() = -kZeroThreshold;
if (max_bin > 2) {
// create zero bin
bin_upper_bound.push_back(kZeroThreshold);
}
}

int right_max_bin = max_bin - static_cast<int>(bin_upper_bound.size());
if ((right_start >= 0) && (right_max_bin > 0)) {
auto right_bounds = GreedyFindBin(distinct_values + right_start, counts + right_start,
num_distinct_values - right_start, right_max_bin, right_cnt_data, min_data_in_bin);
bin_upper_bound.push_back(kZeroThreshold);
bin_upper_bound.insert(bin_upper_bound.end(), right_bounds.begin(), right_bounds.end());
} else {
bin_upper_bound.push_back(std::numeric_limits<double>::infinity());
}
CHECK(bin_upper_bound.size() <= max_bin);
return bin_upper_bound;
}

Expand Down Expand Up @@ -280,6 +290,7 @@ namespace LightGBM {
}
} else if (missing_type_ == MissingType::None) {
bin_upper_bound_ = FindBinWithZeroAsOneBin(distinct_values.data(), counts.data(), num_distinct_values, max_bin, total_sample_cnt, min_data_in_bin);

} else {
bin_upper_bound_ = FindBinWithZeroAsOneBin(distinct_values.data(), counts.data(), num_distinct_values, max_bin - 1, total_sample_cnt - na_cnt, min_data_in_bin);
bin_upper_bound_.push_back(NaN);
Expand Down
19 changes: 19 additions & 0 deletions tests/python_package_test/test_engine.py
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Expand Up @@ -901,6 +901,25 @@ def test_max_bin_by_feature(self):
est = lgb.train(params, lgb_data, num_boost_round=1)
self.assertEqual(len(np.unique(est.predict(X))), 3)

def test_small_max_bin(self):
np.random.seed(0)
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y = np.random.choice([0, 1], 100)
x = np.zeros((100, 1))
x[:30, 0] = -1
x[30:60, 0] = 1
x[60:, 0] = 2
params = {'objective': 'binary',
'seed': 0,
'min_data_in_leaf': 1,
'verbose': -1,
'max_bin': 2}
lgb_x = lgb.Dataset(x, label=y)
est = lgb.train(params, lgb_x, num_boost_round=5)
x[0, 0] = np.nan
params['max_bin'] = 3
lgb_x = lgb.Dataset(x, label=y)
est = lgb.train(params, lgb_x, num_boost_round=5)

def test_refit(self):
X, y = load_breast_cancer(True)
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.1, random_state=42)
Expand Down